package/matchbox: make it a menu

We're about to add a few more options, so it now warrants a menu for
itself.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/matchbox/Config.in

@@ -1,4 +1,4 @@
-config BR2_PACKAGE_MATCHBOX
+menuconfig BR2_PACKAGE_MATCHBOX
 	bool "matchbox"
 	depends on BR2_PACKAGE_XORG7
 	depends on BR2_USE_MMU # fork()